PIC in Sleep

[Electrix]

1. How much current does a PIC draw when in sleep mode ??

2. I have a PIC that is in sleep mode. When its time for work the PC wakes up the PIC and the PIC performs and transfers the data through the Hardware UART and then goes back to sleep. Now the problem is how th wake up the PIC from sleep. I thought of the foll options:
a: Send the external interrupt(RB0/INT) from PC to PIC. (i think it is unreliable)
b: Change on RB input pins. (This is Not in my design)
c: Use the Watch dog timer (My sleep mode is random based..can wake up at any time as desired)

So none of these methods (except the first) suits my design. Are there any other methods i can use ??

 

[Joel Rainville]

1. How much current does a PIC draw when in sleep mode ??

You can probably figure this out by checking the DC characteristics (datasheet) of your PIC. It lists typical current drawn by peripherals used (example from 16F628A datasheet attached). There is quite a difference between VDD at 3 and 5 volts, not to mention between F and LF devices!...

There's also a small paragraph with tips on how to draw minimum current before sending your PIC to sleep, see attached.

a: Send the external interrupt(RB0/INT) from PC to PIC. (i think it is unreliable)

I am just curious. I have read the Wake-up from sleep section in the 16F628A datasheet, and there's no mention of potential problems in any particular cases when using RB0/INT to wake-up the PIC. Why do you believe it'd be unreliable to generate the interrupt externally?

 

[Exo]

1. How much current does a PIC draw when in sleep mode ??

It depends on many things.
First of all you should put all unused pins as outputs, inputs should be pulled high or low. In short - No pins should be left 'floating'.
Switching currents in floating pins will increase power consumtion by a lot (upto mA's !).

The Brown out circuitry also uses quite a lot of current, if you want the absolute minimum you'll have to decide what you want. No Brown out - and the posibility of the pic going nuts when it's supply voltage goes to low. Or with brown out - but even in sleep mode, power consumption will be enough to drain batteries in a couple of weeks.

 

[Joel Rainville]

First of all you should put all unused pins as outputs, inputs should be pulled high or low. In short - No pins should be left 'floating'.

You haven't read the previous post, have you?

The Brown out circuitry also uses quite a lot of current, if you want the absolute minimum you'll have to decide what you want. No Brown out - and the posibility of the pic going nuts when it's supply voltage goes to low. Or with brown out - but even in sleep mode, power consumption will be enough to drain batteries in a couple of weeks.

There are features that will draw even more current than the BOR if left enabled. Check the datasheet!

 

[Exo]

You haven't read the previous post, have you?

No, This forum is SO! big and i have SO! little time :wink: